LABORATORIO. Mollusca EJERCICIO 11. Goals for today

Transcription

1 LABORATORIO Mollusca EJERCICIO 11 Goals for today Learn to recognized the Phylum Mulluska and from other animals Learn the main diagnos=c characteris=cs Learn about some species biology 1

2 Mollusca Mollusca ranks next to arthropods in number of described species ~90,000 species. Mollusca includes chitons, snails, slugs, clams, oyster, squids, octuposes, cuttlefish, and others. Key characteris<cs of the phylum: Body cavity: coelomates Triploblas=c Bilateral symmetry Cephaliza=on Protostomates Ancestral larva trochophore Belong to phylogene=c clade: Lophotrochozoa Muscular foot Protec=ve mantle that houses the gills Typically a shell Porifera Cnidaria and Ctenophora Parazoa Radiata Lophotrochozoa Platyhelminthes Ro=fera Lophophorata Mollusca Annelida Ecdysozoa Deuterostomia Lophotrochozoa Protostomia Eumetazoa Bilateria Exercise 11A: Phylum: Mollusca Clase Bivalvia Genus: Anodonta Anodonta is a freshwater clam. Like many of its freshwater relatives these animals live buried in the sand or mud. Found in rivers, lakes, and streams For the dissection make sure to get a clam with a wooden stick separating the valves otherwise is very difficult to open them 2

3 1. Dissec=on: Take a clam from the container. Examine their external anatomy. Where is the umbo? Freshwater clams are found buried in sand or mud of rivers, streams, and lakes. When you start open it, you need to cut the hinge ligaments and the anterior and posterior adductor muscles, which pull the shell closed 1. Dissec=on: Take a clam from the container. Examine their internal anatomy. 3

4 1. Dissec=on: Take a clam from the container. Examine their internal anatomy. What is the pallial line? 1. Dissec=on: Take a clam from the container. Examine their internal anatomy. If the outer gill is thicker than the inner gill you probably have female. The gill is serving as a brood chamber for developing of the embryos. Are clams monoecious or dioeciuos? Take a look at the labial palps: What do you think is their function? Cut the leg gill, can you see the diges<ve glands? 4

5 1. Dissec=on: Take a clam from the container. Examine their internal anatomy. Do clams have kidneys? 1. Dissec=on: Take a clam from the container. Examine their internal anatomy. Sometimes you can even see the heart (#7). With the exception of most cephalopods, mollusks have an open circulatory system. Where is the body cavity or coelom? The coelom is actually very small and is located around the gonads 5

6 1. Dissec=on: Test yourself Do clams have a brain? 1. Look a bivalve clean shells and iden=fy the following scars 6

7 2. Look for the Glochidia slide in your box. This is the larvae of freshwater clams. Glochidium larva has hooks to by which they fasten themselves to the gills, skin, or scales of passing fish. There they live as parasites for several weeks. They basically used the fish to disperse upstream. After a while the young clam breaks loose and sink to the bottom to develop as a free-living adult. They leave the clam body through the excurrent siphon and are as small a dust particle. Exercise 11D: Phylum: Mollusca Clase Cephalopoda Genus: Loligo Squids are active swimmers. They range in size from a 2 cm up to 15 m! (Giant squid, Architeuthis). Cephalopods have a reduced internal shell of have lost it completely. Take a look at the pluma or internal shell of your squid and the one in the demonstration table. 7

8 Exercise 11D: Phylum: Mollusca Clase Cephalopoda Genus: Loligo Cephalopods have a reduced internal shell of have lost it completely. Take a look at the pluma or internal shell of your squid and the one in the demonstration table. The exception is Nautilus 1. Dissec=on: Before start cumng take a look at the external anatomy of these animals. Look at there skin Squids and cephalopods in general have pigment cells called chromatophores in the skin. What do you think is the function of these cells? What are ommochromes? 8

9 1. Dissec=on: Look at the eyes, the olfactory crest, the pen, and siphon 1. Dissec=on: Ventral view, check out the suckers, eyes, fin, arms, and tentacles, the siphon 9

10 1. Dissec=on: Dorsal View, look at the extension of the pen, the fin, arms and tentacles 1. Dissec=on: If you have a female look for the following structures 10

11 Female Squid In females, the ovaries containing the eggs are light yellow in color; they look and feel like Jell O. Females also have a pair of egg shell glands called nidamental glands; they are the large, oval, white organs located at about the midpoint of the mantle cavity. Females also have an accessory nidamental gland located near the top of the main glands. They are close to the ink sac and pinkish in color, do not confuse them with the heart. 1. Dissec=on: buccal bulb can you find it? 11

12 1. Dissec=on: If you have a male look for the following structures Male Squid In males, The sperm pass through the small coiled tube called the vas deferens and into the spermatophoric gland which looks like a small sac with many intertwining circles within it. This gland adds substances to the sperm to make it into a sperm packet (spermatophore). 12

13 2. Look at a slide of the spermatophores: your instructor will set the slide in the microscope for demonstra=ons Squid don't just make sperm: they package it up into fairly elaborate li\le torpedoes called spermatophores, which are either handed to the female with a specially modified arm called the hectocotyl arm, or squirted onto her with a penis. Once on the female (or a male, it really doesn't ma\er), the spermatophore everts, forming a structure called the spermatangia, in which all the packed sperm uncoil, ready to do their job, and the whole mass is anchored to the target with a cement body. These structures do show speciesspecific differences, but here is one example from Heteroteuthis dispar. machines_of_aggressively_lovin.php 2. Look at a slide of the spermatophores: your instructor will set the slide in the microscope for demonstra=ons Now the curious observa=on: squid are o`en captured festooned with spermatophores and spermatangia, and in many cases, the spermatangia may be imbedded deeply into the musculature of the animal so it's not simply as if the spermatophores are lovingly placed in an appropriate orifice, they are piercing the female (or the male, again, they don't care that much), tearing deep into the interior. The ques<on is, how do they get in there. The answer is that spermatophores also release diges<ve enzymes and ac<vely burrow into the target <ssue. Squid sperm show an aggressive persistence and vigorously ac<ve assault on the female body 13

14 Exercise 11B: Phylum: Mollusca Clase Gastropoda A couple of key characteristics of gastropods include the shell in most species and the phenomenon of torsion. Look at the specimens in the demonstration table can you see the eyes at the top of the tentacles? 1. Look at all the specimens in the table. Take a couple of shells and iden<fy the following parts 14

15 1. One interes<ng aspect of gastropods is the phenomenon of torsion Torsion is an anatomical event which takes place during the very early part of the life of snails and slugs of all kinds. In other words, torsion is a gastropod synapomorphy which occurs in all gastropods during larval development. Torsion is the rotation of the visceral mass, mantle and shell 180 with respect to the head and foot of the gastropod. This brings the mantle cavity and anus to an anterior position above the head. wikipedia 2. Look for a slide in your box labeled as radula The radula an anatomical structure used by molluscs for feeding, sometimes compared to a tongue. It is a minutely toothed, chitinous ribbon, which is typically used for scraping or cutting food before the food enters the esophagus. The radula is unique to the molluscs, and is found in every class of mollusc except the bivalves. wikipedia 15

16 Exercise 11C: Phylum: Mollusca Clase Polyplacophora (chitons) Chitons have shell that is divided into 8 overlapping plates. They feed on algae and diatoms from rocks. Generally live in the intertidal zone. A few species are carnivorous. The mantle in this animals is called the girdle Not all chitons have their plaques in the outside some them buried in their mantle 1. Take a preserved specimen or look at the preserved dissec<on over the demonstra<on table and iden<fy the following parts: Mouth Head Pallial cavity Gills Mantle Foot Anus 16

17 1. Take a preserved specimen or look at the preserved dissec<on over the demonstra<on table and iden<fy the following parts: Links h\p://biog bio.cornell.edu/BioG101_104/tutorials/animals/squid.html h\p://legacy.lclark.edu/~cli`on/marbio/lectures/lecture%2010.html h\p://homepage.uab.edu/acnnnghm/by255l/by255l Mollusca.htm h\p:// school/search.php?search=zoology&tag=true 17